In deep micro technology, the sizes of contact plugs continue to shrink to fit the increasingly reduced gate pitches. To shrink the contact sizes without incurring impact on contact resistance, long contact plugs, as compared to square contact plugs, were adopted. By adopting long contact plugs, the widths of contact plugs, which widths are measured in gate-pitch direction, may be reduced. The long contact plugs have greater lengths, which are measured in gate-routing (gate lengthwise) direction. By using long contact plugs, both active contact sizes and lithography exposure areas are increased.
The long contact plugs can achieve both high gate density and low contact resistance. Concern, however, still exists. For example, line-end shortening and/or line-end to line-end bridging may occur at the ends of neighboring long contact plugs. These may result in either contact-to-fin active opening (also known as contact shortening) or contact-to-contact leakage (caused by contact bridging). To reduce the probability of the line-end shortening, a more limiting space rule is needed to increase the spacing between the ends of neighboring contact plugs, or a more aggressive Optical Proximity Correction (OPC) is needed at line ends. These solutions, however, impact the sizes of integrated circuits. The problem may become worse in future fin-type MOSFETs (3D MOSFETs) since 3D MOSFETs have very narrow active regions.